Method of producing polyamide fine particles, and polyamide fine particles

ABSTRACT

A method produces polyamide fine particles by polymerizing a polyamide monomer (A) in the presence of a polymer (B) at a temperature equal to or higher than the crystallization temperature of a polyamide to be obtained, wherein the polyamide monomer (A) and the polymer (B) are homogeneously dissolved at the start of polymerization, and polyamide fine particles are precipitated after the polymerization. Polyamide fine particles have a number average particle size of 0.1 to 100 μm, a sphericity of 90 or more, a particle size distribution index of 3.0 or less, a linseed oil absorption of 100 mL/100 g or less, and a crystallization temperature of 150° C. or more. In particular, a polyamide having a high crystallization temperature includes fine particles having a smooth surface, a narrow particle size distribution, and high sphericity.

TECHNICAL FIELD

This disclosure relates to a method of producing polyamide fineparticles by a simple method, and polyamide fine particles including apolyamide having a high crystallization temperature, a smooth surface, anarrow particle size distribution, and a high sphericity.

BACKGROUND

Polyamide fine particles are used in a variety of applications such aspowder paints, taking advantage of characteristics such as hightoughness, flexibility, and high heat resistance. In particular,polyamide 12 fine particles made of polyamide 12, having a truespherical shape, solid without pores inside, and having a smooth surfacecan give favorable touch feeling derived from a smooth surface shape inaddition to the flexibility of a resin itself, and are used forhigh-quality cosmetics or paints.

On the other hand, since a polyamide resin with higher crystallizationtemperature such as polyamide 6 or polyamide 66, which has higherversatility and melting point than polyamide 12, may be widely used forhigher heat-resistant applications and the like, irregular and porousfine particles or fine particles with a wide particle size distributionare produced.

Examples of a method of producing polyamide 6 fine particles include amethod of dissolving porous polyamide 6 in a solvent and then adding anon-solvent and water to produce porous polyamide 6 fine particles(Japanese Patent Application Laid-Open Publication No. 2002-80629 andJapanese Patent Application Laid-Open Publication No. 2010-053272).Other examples include a method in which polyamide is strongly stirredin a medium such as polyethylene glycol at a temperature equal to orhigher than the melting point, and a method in which a polycondensationreaction is performed using a polyamide raw material in a silicone oilmedium (Japanese Patent Application Laid-Open Publication No. S60-040134and Japanese Patent Application Laid-Open Publication No. H10-316750).In another method, anionic polymerization is performed in a paraffinmedium to provide irregular polyamide 6 fine particles (Japanese PatentApplication Laid-Open Publication No. S61-181826). A method of producingpolyamide 6 fine particles by anionic polymerization in which a mediumis changed to an aromatic halogen compound and a hydrocarbon polymersolution is also disclosed (Japanese Patent Application Laid-OpenPublication No. H08-073602).

However, since the techniques of Japanese Patent Application Laid-OpenPublication No. 2002-80629 and Japanese Patent Application Laid-OpenPublication No. 2010-053272 lower the solubility in a solvent andprecipitate polyamide, porous fine particles are produced.

In the techniques of Japanese Patent Application Laid-Open PublicationNo. S60-040134 and Japanese Patent Application Laid-Open Publication No.H10-316750, since particles are produced from raw materials that are notmixed, only fine particles having a wide particle size distribution canbe produced.

Regarding the techniques of Japanese Patent Application Laid-OpenPublication No. S61-181826 and Japanese Patent Application Laid-OpenPublication No. H08-073602 by anionic polymerization, since an initiatoris an ignitable and flammable medium and solvent are used, it isdifficult to polymerize at a high temperature, and the solubilitydecreases and the polyamide precipitates in the solvent and, therefore,irregularly shaped fine particles are produced. Furthermore, to remove avariety of media, solvents, and polymers, a complicated process in whicha large amount of organic solvent is necessary is required.

It could therefore be helpful to provide a method of producing polyamidefine particles by a simple method, and polyamide fine particles made ofpolyamide with high crystallization temperature, smooth surface, narrowparticle size distribution, and high sphericity.

SUMMARY

I thus provide:

A method produces polyamide fine particles by polymerizing a polyamidemonomer (A) in the presence of a polymer (B) at a temperature equal toor higher than the crystallization temperature of a polyamide to beobtained, wherein the polyamide monomer (A) and the polymer (B) arehomogeneously dissolved at the start of polymerization, and polyamidefine particles are precipitated after the polymerization.

The polyamide fine particles have the following constitution: that is,polyamide fine particles having a number average particle size of 0.1 to100 μm, a sphericity of 90 or more, a particle size distribution indexof 3.0 or less, a linseed oil absorption of 100 mL/100 g or less, and acrystallization temperature of 150° C. or more.

Preferably, polyamide fine particles are produced further in thepresence of a solvent (C) of the monomer (A) and the polymer (B).

Preferably, the square of the solubility parameter difference betweenthe monomer (A) and the polymer (B) is 0.1 to 25, and the square of thesolubility parameter difference between polyamide and the polymer (B) is0.1 to 16.

Preferably, the solvent (c) is water.

Preferably, the polymer (B) does not include a polar group, or includesany one selected from a hydroxyl group and a sulfhydryl group.

Preferably, the polymer (B) is at least one selected from the groupconsisting of polyethylene glycol, polypropylene glycol,polytetramethylene glycol, polyethylene glycol-polypropylene glycolcopolymer, and an alkyl ether thereof.

Preferably, the molecular weight of the polymer (B) is 500 to 500,000.

In the polyamide fine particles, preferably, polyamide constituting thepolyamide fine particles is any one selected from polyamide 6, polyamide66, and a copolymer thereof.

Preferably, the weight average molecular weight of polyamideconstituting the polyamide fine particles is 8,000 or more.

In the production method, it is possible to produce polyamide having ahigh crystallization temperature as fine particles having a true sphereand a smooth surface by a safe and simple method. Such polyamide fineparticles have high heat resistance and chemical resistance inherent inpolyamides with a high crystallization temperature, as well asslipperiness due to a true spherical shape and smooth surface with anarrow particle size distribution, and therefore can be suitablyutilized for paints, adhesives, inks, toner light diffusing agents,liquid crystal spacers, matting agents, additives for polymer alloy,carriers for a variety of catalysts, chromatographic carriers,automotive parts, aircraft parts, electronic parts, cosmetic additives,medical carriers and the like. The polyamide fine particles can beapplied to a high-performance paint that can be used under harshconditions under which a conventional paint is unusable or the like dueto heat resistance derived from a high crystallization temperature, atrue spherical and smooth surface form, and a uniform particle diameter.Furthermore, in cosmetic applications, the amide group concentration inpolyamide is increased so that the moisture retention is increased, andit is possible to achieve both a smooth and uniform feeling and a moistfeeling due to the true spherical shape and uniform particle size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph of polyamide fine particlesobtained in Example 1.

FIG. 2 is a scanning electron micrograph of polyamide fine particlesobtained in Example 2.

FIG. 3 is a scanning electron micrograph of polyamide fine particlesobtained in Example 8.

FIG. 4 is a scanning electron micrograph of polyamide fine particlesobtained in Example 10.

FIG. 5 is a scanning electron micrograph of polyamide fine particlesobtained in Comparative Example 3.

DETAILED DESCRIPTION

Hereinafter, my methods and fine particles will be described in detail.

My method produces polyamide fine particles by polymerizing a polyamidemonomer (A) in the presence of a polymer (B) at a temperature higherthan the crystallization temperature of the polyamide obtained bypolymerizing the monomer (A), characterized in that the polyamidemonomer (A) and the polymer (B) are homogeneously dissolved at the startof polymerization, and polyamide fine particles are precipitated afterthe polymerization, whereby polyamide fine particles that have truespherical shape, have a smooth surface, are fine, and have a narrowparticle size distribution can be obtained also for a polyamide withhigh crystallization temperature and higher melting point, which hasbeen difficult to obtain by a conventional method.

Whether or not the polyamide monomer (A) at the start of polymerizationis uniformly dissolved in the polymer (B) may be visually confirmed bychecking whether or not a solution in a reaction vessel is transparent.When the polyamide monomer (A) and the polymer (B) are in a state of asuspension or being separated into two phases at the start ofpolymerization, they are incompatible and require formation ofaggregates, strong stirring or the like. In this example, polymerizationmay be started after a solvent (C) is further used to homogenize thepolyamide monomer (A) and the polymer (B). Whether or not the polyamidefine particles are precipitated after the polymerization may be visuallyconfirmed by checking whether or not a liquid in a reaction vessel is asuspension. When the polyamide and the polymer (B) are a homogeneoussolution at the end of polymerization, they are uniformly compatible andbecome aggregates or porous fine particles by cooling or the like.

The polyamide constituting the polyamide fine particles refers to apolymer having a structure containing an amide group, and is produced bya polycondensation reaction of an amino acid which is a monomer (A) ofpolyamide, anionic ring-opening polymerization with a lactam and aninitiator, cationic ring-opening polymerization or ring-openingpolymerization after hydrolysis with water, a polycondensation reactionof a dicarboxylic acid and a diamine or a salt thereof or the like. In alactam, since a homogeneous liquid with the monomer (A) or the polymer(B) by an initiator is not formed and the initiator is ignitable,polymerization at a temperature equal to or higher than thecrystallization temperature of a polyamide in which polyamide fineparticles that have true spherical shape and have smooth surface can beeasily obtained is difficult and, therefore, ring-opening polymerizationwith cationic polymerization or water is preferable, and polymerizationat a temperature equal to or higher than the crystallization temperatureof a polyamide to be obtained is most preferably carried out byring-opening polymerization with water or the like from the viewpointsof coloring the polyamide with an initiator and suppressing cross-linkedproducts or gel products.

Specific examples of the polyamide monomer (A) used as a raw materialfor the polyamide fine particles in the method include a mixtureselected from an amino acid such as aminohexanoic acid, aminoundecanoicacid, aminododecanoic acid, or paramethylbenzoic acid, a lactam such asε-caprolactam and laurolactam, a dicarboxylic acid such as oxalic acid,succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid,undecanedioic acid, dodecanedioic acid, terephthalic acid, isophthalicacid, 1,4-cyclohexanedicarboxylic acid, or 1,3-cyclohexanedicarboxylicacid and a diamine such as ethylenediamine, trimethylenediamine,tetramethylenediamine, pentamethylenediamine, hexamethylenediamine,heptamethylenediamine, octamethylenediamine, nonamethylenediamine,decanediamine, undecanediamine, dodecanediamine, 1,4-cyclohexanediamine,1,3-cyclohexanediamine, 4,4′-diaminodicyclohexylmethane, or3,3′-dimethyl-4,4′-diaminodicyclohexylmethane, and a salt thereof. Twoor more of these monomers (A) may be used as long as they do not impairthe desired result, and another monomer capable of copolymerization maybe included. From the viewpoint that the solubility of the monomer (A)and the polymer (B) is improved, and the resulting polyamide fineparticles have a fine particle size and a narrow particle sizedistribution, aminohexanoic acid, ε-caprolactam, hexamethylenediamine,and adipic acid are preferred, aminohexanoic acid and ε-caprolactam arefurther preferred, and ε-caprolactam is most preferred.

Specific examples of the polyamide produced by polymerizing the monomer(A) include polycaproamide (polyamide 6), polyhexamethylene adipamide(polyamide 66), polytetramethylene adipamide (polyamide 46),polytetramethylene sebacamide (polyamide 410), polypentamethyleneadipamide (polyamide 56), polypentamethylene sebacamide (polyamide 510),polyhexamethylene sebamide (polyamide 610), polyhexamethylene dodecamide(polyamide 612), polydecamethylene adipamide (polyamide 106),polydodecamethylene adipamide (polyamide 126), polydecamethylenesebacamide (polyamide 1010), liundecanamide (polyamide 11),polydodecamide (polyamide 12), polyhexamethylene terephthalamide(polyamide 6T), polydecamethylene terephthalamide (polyamide 10T), andpolycaproamide/polyhexamethylene adipamide copolymer (polyamide 6/66).These may contain another copolymerizable component as long as they donot impair the desired result. In the method, in order that polyamidefine particles to be obtained have a fine particle diameter and a narrowparticle size distribution, and that the heat resistance of thepolyamide constituting the obtained polyamide fine particles isincreased, the crystallization temperature is preferably 150° C. orhigher, and more preferably, the polyamide is selected from any one ofpolyamide 6, polyamide 66, and a copolymer thereof.

The range of the weight average molecular weight of a polyamideconstituting polyamide fine particles is preferably 8,000 to 3,000,000.From the viewpoint of inducing phase separation with the polymer (B),the weight average molecular weight is more preferably 10,000 or more,further preferably 15,000 or more, and most preferably 20,000 or more.Since the viscosity during polymerization depends on the polymer (B), anincrease in viscosity due to an increase in the molecular weight of apolyamide is suppressed. Therefore, there is an advantage that thepolymerization time of a polyamide can be extended and the molecularweight can be extremely increased. However, when the polymerization timeis too long, a side reaction product of polyamide such as a cross-linkedproduct is generated, or deterioration of the polymer (B) occurs and,therefore, the weight average molecular weight of a polyamide is morepreferably 2,000,000 or less, and further preferably 1,000,000 or less.

Note that the weight average molecular weight of a polyamideconstituting polyamide fine particles refers to a weight averagemolecular weight converted from a value measured by gel permeationchromatography with using hexafluoroisopropanol as a solvent in terms ofpolymethyl methacrylate.

The polymer (B) refers to a polymer that dissolves in the polyamidemonomer (A) at the start of polymerization but is incompatible with thepolyamide after polymerization. Dissolution is determined by whether ornot the polymer (B) and the monomer (A) are uniformly dissolved underconditions of temperature and pressure at which polymerization isstarted. The incompatibility between the polymer (B) and the polyamideis determined by whether they are a suspension or separated into twophases under temperature and pressure conditions after polymerization.Determination as to whether the solution is a homogeneous solution,suspension, or two-phase separation can be made by visually checking areaction vessel.

More specifically, the polymer (B) is preferably non-reactive with apolyamide monomer from the viewpoint of precipitating polyamide fineparticles from a uniform solution. In particular, the polymer (B)preferably does not include a polar group that reacts with a carboxylgroup or an amino group that forms an amide group of polyamide, orpreferably includes a polar group with low reactivity with a carboxylgroup or an amino group. Examples of a polar group that reacts with acarboxyl group or an amino group include an amino group, a carboxylgroup, an epoxy groups, and an isocyanate group. Examples of the polargroup having low reactivity with a carboxyl group or an amino groupinclude a hydroxyl group and a sulfhydryl group, and from the viewpointof suppressing a cross-linking reaction, the number of polar groups inthe polymer (B) is preferably 4 or less, more preferably 3 or less, andmost preferably 2 or less.

The polymer (B) is preferably incompatible with polyamide but has highaffinity from the viewpoint of making polyamide fine particles to begenerated finer and having high solubility in the monomer (A) andnarrowing the particle size distribution. In other words, regarding theaffinity between monomer (A) and polymer (B) or the affinity betweenpolymer (B) and polyamide, when solubility parameters (hereinafter,referred to as SP values) are set to δ_(A), δ_(B), and δ_(PA)(J^(1/2)/cm^(3/2)), respectively, the affinity between the monomer (A)and the polymer (B) can be expressed by the square of the solubilityparameter difference, or (δ_(A)−δ_(B))², and the affinity between thepolymer (B) and the polyamide can be expressed by the square of thesolubility parameter difference, or (δ_(PA)−δ_(B))². The closer thevalue is to zero, the higher the affinity and the higher the solubilityor compatibility, and since δ_(A) and δ_(PA) of the monomer (A) and thepolyamide are different from each other, the polyamide is difficult tobecome an aggregate, and from the viewpoint of preventing the polymer(B) from being dissolved in the monomer (A) and generating an aggregate,(δ_(A)−δ_(B))² preferably satisfies the range of 0.1 to 25. The lowerlimit of (δ_(A)−δ_(B))² is more preferably 0.3 or more, furtherpreferably 0.5 or more, and particularly preferably 1 or more. The upperlimit of (δ_(A)−δ_(B))² is more preferably 16 or less, furtherpreferably 12 or less, particularly preferably 10 or less, and mostpreferably 7 or less. On the other hand, from the viewpoint ofpreventing the polymer (B) from being uniformly compatible andpreventing polyamide fine particles from being unobtainable, whilepreventing the polyamide from becoming incompatible and becoming anaggregate, (δ_(PA)−δ_(B))² preferably satisfies the range of 0.1 to 16.The lower limit of (δ_(PA)−δ_(B))² is more preferably 0.3 or more,further preferably 0.5 or more, and particularly preferably 1 or more.The upper limit of (δ_(PA)−δ_(B))² is more preferably 12 or less,further preferably 10 or less, particularly preferably 7 or less, andmost preferably 4 or less.

The SP value is a value calculated from the cohesive energy density andmolar molecular volume of Hoftyzer-Van Krevelen described in Propertiesof Polymers 4th Edition (D. W. Van Krevelen, published by ElsevierScience 2009), Chapter 7, p 215. When the calculation cannot beperformed by this method, a value calculated from the cohesive energydensity of Fedors described in the same chapter p 195 and the molarmolecular volume is shown. When two or more types of monomers (A) andpolymers (B) are used, a value obtained by adding the products of therespective SP values and molar fractions is shown.

Specific examples of such a polymer (B) include an alkyl ether in whichpolyethylene glycol, polypropylene glycol, polytetramethylene glycol,polypentamethylene glycol, polyhexamethylene glycol, polyethyleneglycol-polypropylene glycol copolymer, or polyethyleneglycol-polytetramethylene glycol copolymer and a hydroxyl group at oneor both ends thereof are blocked with a methyl group, an ethyl group, apropyl group, an isopropyl group, a butyl group, a hexyl group, an octylgroup, a decyl group, a dodecyl group, a hexadecyl group, or anoctadecyl group, and an alkylphenyl ether in which an octylphenyl groupis blocked. In particular, from the viewpoint of excellent compatibilitywith the polyamide monomer (A) and narrowing the particle sizedistribution of polyamide fine particles to be obtained, polyethyleneglycol, polyethylene glycol-polypropylene glycol copolymer,polypropylene glycol, and polytetramethylene glycol, and these alkylethers are preferable, and from the viewpoint of excellent compatibilitywith water used as a solvent for ring-opening polymerization byhydrolysis of the polyamide monomer (A), polyethylene glycol andpolyethylene glycol-polypropylene glycol copolymers are more preferable,and polyethylene glycol is most preferable. Two or more of these may beused at the same time as long as the desired result is not impaired.

From the viewpoint of preventing from extremely slow reaction rate ofpolyamide polymerization due to overhigh viscosity of a uniformsolution, while the particle size and particle size distribution ofpolyamide fine particles to be obtained can be narrowed, the upper limitof the weight average molecular weight of a polymer (B) is preferably500,000, more preferably 100,000 or less, and further preferably 50,000or less. From the viewpoint of preventing formation of polyamide fineparticles from being difficult due to excessive improvement in thecompatibility between the polymer (B) and the polyamide, the weightaverage molecular weight of the polymer (B) is preferably 500 or more,more preferably 1,000 or more, and further preferably 2,000 or more.

The weight average molecular weight of the polymer (B) refers to theweight average molecular weight in terms of polyethylene glycol asmeasured by gel permeation chromatography using water as a solvent. Whenthe polymer (B) does not dissolve in water, the weight average molecularweight of the polymer (B) refers to the weight average molecular weightin terms of polystyrene measured by gel permeation chromatography usingtetrahydrofuran as a solvent.

Polyamide fine particles are produced by mixing these monomers (A) andpolymer (B) to obtain a homogeneous solution and then polymerizingmonomer (A) to initiate polymerization at a temperature higher than thecrystallization temperature of a polyamide to be obtained. At this time,as the monomer (A) is converted to polyamide in a uniform mixedsolution, polyamide fine particles are uniformly induced withoutcrystallization, it is considered that polyamide fine particles with atrue spherical shape, smooth surface, fineness, and narrow particle sizedistribution are precipitated after polymerization.

From the viewpoint of preventing formation of a large amount ofaggregates because particle formation occurs from the early stage ofpolymerization, while the polymerization rate is moderate, and phaseseparation induced with polymerization occurs and particle formationoccurs smoothly, the mass ratio of the monomer (A) and the polymer (B)when polymerizing is preferably 5/95 to 80/20. The lower limit of themass ratio of monomer (A)/polymer (B) is more preferably 10/90, furtherpreferably 20/80, and most preferably 30/70. On the other hand, theupper limit of the mass ratio of monomer (A)/polymer (B) is morepreferably 70/30, further preferably 60/40, and particularly preferably50/50.

As a method of polymerizing the monomer (A) to polyamide, a known methodcan be used. The method depends on the type of monomer (A), and in alactam, anionic ring-opening polymerization using an alkali metal suchas sodium or potassium or an organometallic compound such as butyllithium or butyl magnesium as an initiator, cationic ring-openingpolymerization using an acid as an initiator, hydrolytic ring-openingpolymerization using water and such or the like is generally used.Cationic ring-opening polymerization and hydrolytic ring-openingpolymerization are preferable because polymerization can be performed ata temperature equal to or higher than the crystallization temperature ofthe polyamide, which is easy to obtain true spherical and smoothpolyamide fine particles, and hydrolytic ring-opening polymerization ismore preferable from the viewpoint of suppressing coloring of apolyamide by an initiator and gelation or a decomposition reaction dueto a crosslinking reaction in polymerization at a temperature higherthan the crystallization temperature of the polyamide to be obtained. Amethod of ring-opening polymerization of a lactam by hydrolysis is notlimited as long as the method is a known method, and a method in whichpressure is applied in the presence of water to generate an amino acidwhile promoting lactam hydrolysis, and then ring-opening polymerizationand polycondensation reaction are performed while removing water ispreferred.

In this example, since a polycondensation reaction does not occur ifwater is present, polymerization starts at the same time as the water isdischarged out of the reaction vessel. Accordingly, the amount of waterused is not particularly limited as long as hydrolysis of a lactamproceeds, and usually, when the total amount of the monomer (A) and thepolymer (B) is 100 parts by mass, the amount of water used is preferably100 parts by mass or less. To improve the production efficiency ofpolyamide fine particles, the amount of water used is more preferably 70parts by mass or less, further preferably 50 parts by mass or less, andparticularly preferably 30 parts by mass or less. To prevent ahydrolysis reaction of a lactam from proceeding, the lower limit of theamount of water used is preferably 1 part by mass or more, morepreferably 2 parts by mass or more, further preferably 5 parts by massor more, and particularly preferably 10 parts by mass or more. As amethod of removing water (condensation water) generated by condensationduring polycondensation, a known method such as a method of removingwater while flowing an inert gas such as nitrogen at normal pressure ora method of removing water under reduced pressure can be used asappropriate.

When the monomer (A) is an amino acid, dicarboxylic acid and diamine, ora salt thereof, a polycondensation reaction can be used as apolymerization method. On the other hand, in these monomers (A), thereis a combination in which dissolution with the polymer (B) does notoccur uniformly. Regarding such monomer (A) and polymer (B), it ispossible to produce polyamide fine particles by further adding a solvent(C) of the monomer (A) and the polymer (B).

The solvent (C) is not particularly limited as long as it is in theabove range, and water is most preferable because it is the same ascondensed water that needs to be discharged out of a system to dissolvethe monomer (A) and the polymer (B) and to proceed a polycondensationreaction.

In particular, when using an amino acid such as aminohexanoic acid oraminododecanoic acid for the monomer (A), or when using a dicarboxylicacid and a diamine such as adipic acid and hexamethylenediamine for themonomer (A), by adding polyethylene glycol, polyethyleneglycol-polypropylene glycol copolymers, and an alkyl ether thereof asthe polymer (B) and water as the solvent (C), a uniform solution isformed at the temperature at which polymerization starts. After that, bydischarging condensed water generated by progress of polycondensationwith water as the solvent (C) out of a reaction vessel, polyamide fineparticles can be produced while polymerization proceeds. In thisexample, when the total amount of amino acid or dicarboxylic acid,diamine, and the polymer (B) is set to 100 parts by mass, the amount ofwater used as the solvent (C) is preferably 10 to 200 parts by mass.From the viewpoint of preventing the particle diameter from becomingcoarse, the amount of water used is more preferably 150 parts by mass orless, and further preferably 120 parts by mass or less. On the otherhand, from the viewpoint of ensuring that water functions as a solvent,the amount of water used is preferably 20 parts by mass or more, andfurther preferably 40 parts by mass or more.

Two or more lactams and amino acids and/or dicarboxylic acids ordiamines may be used in mixture, and in this example, water functionsfor hydrolysis or as a solvent (C).

The polymerization temperature is not particularly limited as long asthe polymerization of polyamide proceeds, and from the viewpoint ofcontrolling a polyamide having a high crystallization temperature closerto a true sphere and having a smooth surface, the polymerizationtemperature is preferably set to a temperature equal to or higher thanthe crystallization temperature of polyamide to be obtained. Thepolymerization temperature is more preferably the crystallizationtemperature of a polyamide to be obtained +15° C. or higher, furtherpreferably the crystallization temperature of a polyamide to be obtained+30° C. or higher, and particularly preferably the crystallizationtemperature of a polyamide to be obtained +45° C. or higher. From theviewpoint of preventing a side reaction of a polyamide such as athree-dimensional cross-linked product and progression of coloring ordeterioration of the polymer (B), the polymerization temperature ispreferably the melting point of a polyamide to be obtained +100° C. orless, more preferably the melting point of a polyamide to be obtained+50° C. or less, further preferably the melting point of a polyamide tobe obtained +20° C. or less, particularly preferably the melting pointof a polyamide to be obtained, and most preferably the melting point ofa polyamide to be obtained −10° C. or lower.

The crystallization temperature of a polyamide constituting polyamidefine particles refers to the apex of an exothermic peak which appearswhen the temperature is raised from 30° C. to the temperature 30° C.higher than the endothermic peak indicating the melting point of thepolyamide at a rate of 20° C./min using a DSC method, thereafter holdingfor 1 minute, and then cooled to 30° C. at a rate of 20° C./min. Thepeak of an endothermic peak when the temperature is further raised at arate of 20° C./min after cooling is set to the melting point ofpolyamide fine particles.

The polymerization time can be appropriately adjusted according to themolecular weight of polyamide fine particles to be obtained, and fromthe viewpoint of preventing progression of a side reaction and coloringof the polyamide such as a three-dimensional cross-linked product anddeterioration of the polymer (B) while ensuring that polymerizationproceeds to obtain polyamide fine particles, the polymerization time isusually preferably 0.1 to 70 hours. The lower limit of thepolymerization time is more preferably 0.2 hours or more, furtherpreferably 0.3 hours or more, and particularly preferably 0.5 hours ormore. The upper limit of the polymerization time is more preferably 50hours or less, further preferably 25 hours or less, and particularlypreferably 10 hours or less.

A polymerization accelerator may be added as long as the desired effectis not impaired. As the accelerator, a known one can be used, andexamples thereof include an inorganic phosphorus compound such asphosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoricacid, polyphosphoric acid, and an alkali metal salt and an alkalineearth metal salt thereof. Two or more of these may be used. The amountof each addition can be appropriately selected, and it is preferable toadd 1 part by mass or less with respect to 100 parts by mass of themonomer (A).

Another additive may be added, and examples thereof include a surfactantto control the particle size of polyamide fine particles, a dispersant,and an antioxidant, a heat stabilizer, a weathering agent, a lubricant,a pigment, a dye, a plasticizer, an antistatic agent, and a flameretardant to improve the properties of polyamide fine particles andimprove the stability of the polymer (B) to be used. Two or more ofthese may be used. Two or more different types may be used for thepurpose of modifying the monomer (A) or polyamide and for the purpose ofmodifying the polymer (B). The amount of each addition can beappropriately selected, and it is preferable to add 1 part by mass orless with respect to 100 parts by mass in total of the monomer (A) andthe polymer (B).

Since polyamide fine particles are homogeneously induced from ahomogeneous solution, tiny fine particles can be produced withoutperforming stirring, but stirring may be performed to further controlthe particle size and make the particle size distribution more uniform.As a stirring device, a known device such as a stirring blade, a meltkneader, or a homogenizer can be used, and in a stirring blade, examplesthereof include a propeller-, paddle-, flat-, turbine-, cone-, anchor-,screw-, and helical-type. The stirring speed depends on the type andmolecular weight of the polymer (B), the stirring speed is preferably 0to 2,000 rpm from the viewpoint of uniformly transferring heat even in alarge apparatus and preventing a liquid from adhering to the wallsurface to change the blending ratio. The lower limit of the stirringspeed is more preferably 10 rpm or more, further preferably 30 rpm ormore, particularly preferably 50 rpm or more, and the upper limit of thestirring speed is more preferably 1,600 rpm or less, further preferably1,200 rpm or less, and particularly preferably 800 rpm or less.

Examples of the method of isolating polyamide fine particles from amixture of the polyamide fine particles and the polymer (B) aftercompletion of polymerization include a method of isolating afterdischarging a mixture at the completion of polymerization into a poorsolvent for polyamide fine particles and a method of isolating afteradding a poor solvent for polyamide fine particles in a reaction vessel.From the viewpoint of preventing polyamide fine particles from meltingand coalescing to broaden the particle size distribution, a method ofisolating by discharging a mixture into a poor solvent for polyamidefine particles after cooling to the melting point of the polyamide fineparticles or lower, more preferably the crystallization temperature orlower or a method of isolating by adding a poor solvent for polyamidefine particles to a reaction vessel is preferable, and a method ofisolating by adding a poor solvent for polyamide fine particles to areaction vessel is more preferable. As the isolation method, a knownmethod such as reduced pressure, pressure filtration, decantation,centrifugation, spray drying or the like can be appropriately selected.

The poor solvent for polyamide fine particles is preferably a solventthat does not dissolve a polyamide but further dissolves the monomer (A)or the polymer (B). Such a solvent can be appropriately selected, and analcohol such as methanol, ethanol or isopropanol, or water is preferred.

Washing, isolation, and drying of polyamide fine particles can becarried out by a known method. As the washing method of removing adeposit and inclusion on polyamide fine particles, reslurry cleaning orthe like can be used, and heating may be performed as appropriate. Thesolvent used for washing is not limited as long as it does not dissolvepolyamide fine particles and dissolves the monomer (A) or the polymer(B), and methanol, ethanol, isopropanol, or water is preferable from theviewpoint of economy, and water is most preferable. The isolation methodcan be appropriately selected from reduced pressure, pressurefiltration, decantation, centrifugation, spray drying and the like.Drying is preferably carried out at the melting point of polyamide fineparticles or lower, and may be carried out under reduced pressure. Airdrying, hot air drying, heat drying, reduced pressure drying, freezedrying or the like is selected.

Polyamide fine particles are produced by the above method. It is thuspossible to produce polyamide fine particles having a highcrystallization temperature, which has hitherto been difficult, with auniform particle diameter, a true spherical shape, and a smooth surface.

The high crystallization temperature polyamide constituting polyamidefine particles refers to a crystalline polyamide having acrystallization temperature of 150° C. or higher. From the viewpoint ofincreasing the melting point, chemical resistance or the like due tocrystallinity and obtaining a polyamide with higher heat resistance, thecrystallization temperature of a polyamide is preferably 160° C. orhigher, more preferably 170° C. or higher, and further preferably 180°C. or higher. From the viewpoint of preventing the shape from becomingporous, the crystallization temperature of the polyamide is preferably300° C. or less, more preferably 280° C. or less, and particularlypreferably 260° C. or less.

Specific examples of the high crystallization temperature polyamideinclude polycaproamide (polyamide 6), polyhexamethylene adipamide(polyamide 66), polytetramethylene adipamide (polyamide 46),polytetramethylene sebacamide (polyamide 410), polypentamethyleneadipamide (polyamide 56), polypentamethylene sebacamide (polyamide 510),polyhexamethylene sebacamide (polyamide 610), polyhexamethylenedodecamide (polyamide 612), polydecamethylene adipamide (polyamide 106),polydodecamethylene adipamide (polyamide 126), polyhexamethyleneterephthalamide (polyamide 6T), polydecamethylene terephthalamide(polyamide 10T), and polycaproamide/polyhexamethylene adipamidecopolymer (polyamide 6/66), and preferred is polycaproamide (polyamide6), polyhexamethylene adipamide (polyamide 66), polyhexamethylenesebacamide (polyamide 610), polyhexamethylene dodecamide (polyamide612), polydecamethylene adipamide (polyamide 106), polydodecamethyleneadipamide (polyamide 126), or polycaproamide/polyhexamethylene adipamidecopolymer (polyamide 6/66), and more preferred is polycaproamide(polyamide 6), polyhexamethylene adipamide (polyamide 66), orpolycaproamide/polyhexamethylene adipamide copolymer (polyamide 6/66).

The number average particle size of the polyamide fine particles is 0.1to 100 μm. When the number average particle size exceeds 100 μm, thesurface of a coating film prepared from the particles becomesinhomogeneous. The number average particle size of polyamide fineparticles is preferably 80 μm or less, more preferably 60 μm or less,further preferably 50 μm or less, and particularly preferably 30 μm orless. When the number average particle size is less than 0.1 μm,aggregation of particles occurs. The number average particle size ofpolyamide fine particles is preferably 0.3 μm or more, more preferably0.7 μm or more, further preferably 1 μm or more, particularly preferably2 μm or more, and most preferably 3 μm or more.

The particle size distribution index indicating the particle sizedistribution of the polyamide fine particles is 3.0 or less. When theparticle size distribution index exceeds 3.0, the fluidity is inferiorin paint or cosmetic applications, and the uniformity of a coating filmsurface is impaired. The particle size distribution index is preferably2.0 or less, more preferably 1.5 or less, further preferably 1.3 orless, and most preferably 1.2 or less. The lower limit is theoretically1.

The number average particle size of polyamide fine particles can becalculated by specifying 100 particle diameters randomly from a scanningelectron micrograph and calculating the arithmetic average thereof. Inthe above micrograph, when the shape is not a perfect circle, or theshape is oval for example, the maximum diameter of the particle is takenas the particle diameter. To accurately measure the particle size,measurement is carried out at a magnification of at least 1,000 times,and preferably at least 5,000 times. The particle size distributionindex is determined based on the following numerical conversion formulafor the particle size value obtained above.

$\begin{matrix}{D_{n} = {\left( {\sum\limits_{i = 1}^{n}D_{i}} \right)/n}} & {D_{v} = {\sum\limits_{i = 1}^{n}{D_{i}^{4}/{\sum\limits_{i = 1}^{n}D_{i}^{3}}}}} & {{PDI} = {D_{v}/D_{n}}}\end{matrix}$

Di: particle diameter of each particle, n: number of measurements 100,Dn: number average particle size, Dv: volume average particle size, andPDI: particle size distribution index.

Since the polyamide fine particles have a smooth shape in addition to atrue spherical shape, it is possible to impart favorable slipperinessand fluidity to cosmetics and paints.

The sphericity indicating the sphericity of polyamide fine particles is90 or more. When the sphericity is less than 90, it is not possible toimpart a smoother feel in cosmetics and paint applications. Thesphericity is preferably 95 or more, more preferably 97 or more, andfurther preferably 98 or more. The upper limit thereof is 100.

The sphericity of polyamide fine particles is determined by observing 30particles randomly from a scanning electron micrograph and determining ashort diameter and a long diameter according to the following formula.

$S = {\sum\limits_{i = 1}^{n}{\left( {b/a} \right)/n}}$

S: sphericity, a: major axis, b: minor axis, and n: number ofmeasurements is 30.

The smoothness of the surface of polyamide fine particles can beexpressed by the amount of linseed oil absorbed by the polyamide fineparticles. In other words, the smoother the surface, the smaller thenumber of pores on the surface is, and the smaller the linseed oilabsorption indicating the amount of linseed oil absorbed is. The linseedoil absorption of the polyamide fine particles is 100 mL/100 g or less.When the linseed oil absorption of polyamide fine particles exceeds 100mL/100 g, favorable fluidity cannot be imparted to cosmetics and paints.The linseed oil absorption of polyamide fine particles is preferably 90mL/100 g or less, more preferably 80 mL/100 g or less, furtherpreferably 70 mL/100 g or less, and particularly preferably 60 mL/100 gor less. The lower limit of the linseed oil absorption is 0 mL/100 g ormore.

The linseed oil absorption is measured in accordance with JapaneseIndustrial Standard (JIS Standard) JIS K 5101 “Pigment Test Method,Refined Linseed Oil Method”.

The smoothness of the surface can also be expressed by the BET specificsurface area by gas adsorption, and the smoother the surface, thesmaller the BET specific surface area. Specifically, the BET specificsurface area is preferably 10 m²/g or less, more preferably 5 m²/g orless, further preferably 3 m²/g or less, particularly preferably 1 m²/gor less, and most preferably 0.5 m²/g or less.

The BET specific surface area is measured in accordance with JapaneseIndustrial Standard (JIS standard) JIS R 1626 (1996) “Method formeasuring specific surface area by gas adsorption BET method”.

EXAMPLES

Hereinafter, my methods and fine particles will be described by way ofExamples, but this disclosure is not limited thereto.

(1) Average Particle Size and Particle Size Distribution Index

The number average particle size of polyamide fine particles wascalculated by specifying 100 particle diameters randomly from a scanningelectron micrograph and calculating the arithmetic average thereof. Inthe above micrograph, when the shape was not a perfect circle or theshape was oval, for example, the maximum diameter of the particle wastaken as the particle diameter. The particle size distribution index wascalculated based on the following numerical conversion formula for theparticle size value obtained above.

$\begin{matrix}{D_{n} = {\left( {\sum\limits_{i = 1}^{n}D_{i}} \right)/n}} & {D_{v} = {\sum\limits_{i = 1}^{n}{D_{i}^{4}/{\sum\limits_{i = 1}^{n}D_{i}^{3}}}}} & {{PDI} = {D_{v}/D_{n}}}\end{matrix}$

Di: particle diameter of each particle, n: number of measurements 100,Dn: number average particle size, Dv: volume average particle size, andPDI: particle size distribution index.

(2) Sphericity

The sphericity of polyamide fine particles was calculated by observing30 particles randomly from a scanning electron micrograph anddetermining a short diameter and a long diameter according to thefollowing formula.

$S = {\sum\limits_{i = 1}^{n}{\left( {b/a} \right)/n}}$

S: sphericity, a: major axis, b: minor axis, and n: number ofmeasurements is 30.

(3) Linseed Oil Absorption

In accordance with Japanese Industrial Standard (JIS Standard) JIS K5101 “Pigment Test Method Refined Linseed Oil Method”, about 100 mg ofpolyamide fine particles were precisely weighed on a watch glass,refined linseed oil (manufactured by KANTO CHEMICAL CO., INC.) wasgradually added with a burette drop by drop, kneaded with a paletteknife, then dripping-kneading was repeated until a sample lump wasformed, the oil absorption (mL/100 g) was calculated from the amount ofrefined linseed oil used for dropping, with the point at which the pastehad smooth hardness as the completion point.

(4) BET Specific Surface Area

In accordance with Japanese Industrial Standard (JIS Standard) JIS R1626 (1996) “Method for Measuring Specific Surface Area by GasAdsorption BET Method”, using BELSORP-max manufactured by BEL JAPANINC., about 0.2 g of polyamide fine particles were put into a glass celland degassed under reduced pressure at 80° C. for about 5 hours, then akrypton gas adsorption isotherm at liquid nitrogen temperature wasmeasured, and the BET specific surface area was calculated by the BETmethod.

(5) Crystallization Temperature and Melting Point of PolyamideConstituting Polyamide Fine Particles

The apex of an exothermic peak which appears when the temperature israised from 30° C. to the temperature 30° C. higher than the endothermicpeak indicating the melting point of the polyamide at a rate of 20°C./min using a differential scanning calorimeter (DSCQ20) manufacturedby TA Instruments Japan Inc., thereafter holding for 1 minute, and thencooled to 30° C. at a rate of 20° C./min was defined as thecrystallization temperature. The peak of an endothermic peak when thetemperature is further raised at a rate of 20° C./min after cooling wasset to the melting point. The amount of polyamide fine particlesrequired for measurement was about 8 mg.

(6) Molecular Weight of Polyamide Constituting Polyamide Fine Particles

The weight average molecular weight of polyamide was calculated by usinga gel permeation chromatography method and comparison with a calibrationcurve of polymethyl methacrylate. A measurement sample was prepared bydissolving about 3 mg of polyamide fine particles in about 3 g ofhexafluoroisopropanol.

-   -   Apparatus: WATERS E-ALLIANCE GPC SYSTEM    -   Column: Manufactured by Showa Denko K.K., HFIP-806M×2    -   Mobile phase: 5 mmol/L Sodium        trifluoroacetate/hexafluoroisopropanol    -   Flow velocity: 1.0 mL/min.    -   Temperature: 30° C.    -   Detection: Differential refractometer.        (7) Molecular Weight of Polymer (B)

The weight average molecular weight of the polymer (B) was calculated byusing a gel permeation chromatography method and comparison with acalibration curve using polyethylene glycol. A measurement sample wasprepared by dissolving about 3 mg of the polymer (B) in about 6 g ofwater.

-   -   Apparatus: Manufactured by Shimadzu Corporation, LC-10A series    -   Column: Manufactured by Tosoh Corporation, TSKgelG3000PWXL    -   Mobile phase: 100 mmol/L Sodium chloride aqueous solution    -   Flow velocity: 0.8 mL/min.    -   Temperature: 40° C.    -   Detection: Differential refractometer.

Example 1

4 g of ε-caprolactam (special grade manufactured by Wako Pure ChemicalIndustries, Ltd., SP value 19.5), 6 g of polyethylene glycol (firstgrade polyethylene glycol 6,000, molecular weight 7,700, SP value 21.3,manufactured by Wako Pure Chemical Industries, Ltd.), and 10 g of waterfor hydrolysis were added to a 100 mL autoclave, and after sealing theautoclave, replacement with nitrogen was performed up to 10 kg/cm². Thesystem pressure was adjusted to 0.1 kg/cm² while releasing nitrogen, andthen the temperature was raised to 240° C. At this time, after thesystem pressure reached 10 kg/cm², water vapor was controlled to beslightly released so that the pressure was maintained at 10 kg/cm².After the temperature reached 240° C., polymerization was started byreleasing the pressure at a rate of 0.2 kg/cm² min. At this point, theinner solution was uniformly transparent. While raising the temperatureto 255° C., the pressure in the system was reduced to 0 kg/cm², and atthe same time, heating was maintained while flowing nitrogen for 3 hoursto complete the polymerization. After polymerization, the inner solutionwas suspended. Nitrogen was again filled to 10 kg/cm² and then cooled toroom temperature. Water was added to the obtained solid and heated to80° C. to dissolve the dissolved matter. The obtained slurry wasfiltered, and 40 g of water was added to the filtered product, followedby washing at 80° C. A slurry liquid without an aggregate filteredthrough a 200 μm sieve was then filtered again and the filtered productisolated was dried at 80° C. for 12 hours to obtain 2.8 g of powder.There were no aggregates greater than 200 μm. The obtained powder had amelting point of 214° C. similar to that of polyamide 6, acrystallization temperature of 172° C., and a molecular weight of38,000. From scanning electron microscope observation, polyamide 6powder had a true spherical fine particle shape, a number averageparticle size of 6.6 μm, a particle size distribution index of 1.08, asphericity of 96, a linseed oil absorption of 57 mL/100 g, and a BETspecific surface area of 1.0 m²/g. The SP value of polyamide 6 is 21.9.FIG. 1 shows a scanning electron micrograph (magnification×3,000) of thetrue spherical polyamide 6 fine particles. Table 1 shows the propertiesof the obtained polyamide 6 fine particles.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Example 8 Polyamide constituting poly- poly- poly- poly- poly-poly- poly- poly- polyamide fine particles amide 6 amide 6 amide 6 amide6 amide 6 amide 6 amide 6 amide 6 Weight average molecular 38,000 44,10026,800 35,600 32,500 41,700 38,000 40,200 weight of polyamideconstituting polyamide fine particles Number average particle size of(μm) 6.6 12.9 5.3 6.1 3.5 6.1 21.5 31.5 polyamide fine particlesSphericity of polyamide fine 96 95 95 92 93 93 91 90 particles Particlesize distribution index of 1.08 1.76 1.24 1.23 1.15 1.34 1.92 2.76polyamide fine particles Linseed oil adsorption amount (mL/100 g) 57 5459 60 59 53 65 63 of polyamide fine particles Melting point of polyamidefine (° C.) 214 216 213 211 210 212 216 214 particles Crystallizationtemperature of (° C.) 172 169 172 170 175 171 170 169 polyamide fineparticles

Example 2

Polymerization was carried out in the same manner as in Example 1 exceptthat ε-caprolactam was changed to 5 g and polyethylene glycol (firstgrade polyethylene glycol 6,000 manufactured by Wako Pure ChemicalIndustries, Ltd.) was changed to 5 g to obtain 0.7 g of powder. Thesolution was a homogeneous solution at the start of polymerization, anda suspension after polymerization. The obtained powder had a meltingpoint of 216° C. similar to that of polyamide 6, a crystallizationtemperature of 169° C., and a molecular weight of 44,100. From scanningelectron microscope observation, polyamide 6 powder had a true sphericalshape and a fine particle shape with a smooth surface, a number averageparticle size of 12.9 μm, a particle size distribution index of 1.76, asphericity of 95, and a linseed oil absorption of 54 mL/100 g. FIG. 2shows a scanning electron micrograph (magnification×1,000) of the truespherical polyamide 6 fine particles. Table 1 shows the properties ofthe obtained polyamide 6 fine particles.

Example 3

Polymerization was carried out in the same manner as in Example 1 exceptthat ε-caprolactam was changed to 2 g and polyethylene glycol (firstgrade polyethylene glycol 6,000 manufactured by Wako Pure ChemicalIndustries, Ltd.) was changed to 8 g to obtain 1.5 g of powder. Thesolution was a homogeneous solution at the start of polymerization and asuspension after polymerization. The obtained powder had a melting pointof 213° C. similar to that of polyamide 6, a crystallization temperatureof 172° C., and a molecular weight of 26,800. From scanning electronmicroscope observation, polyamide 6 powder had a true spherical shapeand a fine particle shape with a smooth surface, a number averageparticle size of 5.3 μm, a particle size distribution index of 1.24, asphericity of 95, and a linseed oil absorption of 59 mL/100 g. Table 1shows the properties of the obtained polyamide 6 fine particles.

Example 4

Polymerization was carried out in the same manner as in Example 1 exceptthat a polyethylene glycol (Wako Pure Chemical Industries, Ltd., firstgrade polyethylene glycol 20,000, molecular weight 18,600, SP value21.3) having a different molecular weight was used to obtain 3.3 g of apowder. The solution was a homogeneous solution after thepolymerization, and was a suspension solution at the end of thepolymerization. The obtained powder had a melting point of 211° C.similar to that of polyamide 6, a crystallization temperature of 170°C., and a molecular weight of 35,600. From scanning electron microscopeobservation, polyamide 6 powder had a true spherical shape and a fineparticle shape with a smooth surface, a number average particle size of6.1 μm, a particle size distribution index of 1.23, a sphericity of 92,and a linseed oil absorption of 60 mL/100 g. Table 1 shows theproperties of the obtained polyamide 6 fine particles.

Example 5

Polymerization was carried out in the same manner as in Example 1 exceptthat a polyethylene glycol (Wako Pure Chemical Industries, Ltd., firstgrade polyethylene glycol 35,000, molecular weight 31,000, SP value21.3) having a different molecular weight was used to obtain 2.1 g of apowder. The solution was a homogeneous solution at the start ofpolymerization and a suspension after polymerization. The obtainedpowder had a melting point of 210° C. similar to that of polyamide 6, acrystallization temperature of 175° C., and a molecular weight of32,500. From scanning electron microscope observation, polyamide 6powder had a true spherical shape and a fine particle shape with asmooth surface, a number average particle size of 3.5 μm, a particlesize distribution index of 1.15, a sphericity of 93, and a linseed oilabsorption of 59 mL/100 g. Table 1 shows the properties of the obtainedpolyamide 6 fine particles.

Example 6

Polymerization was carried out in the same manner as in Example 1 exceptthat a polyethylene glycol (Wako Pure Chemical Industries, Ltd., firstgrade polyethylene glycol 2,000, molecular weight 2,300, SP value 21.3)having a different molecular weight was used to obtain 2.3 g of apowder. The solution was a homogeneous solution at the start ofpolymerization and a suspension after polymerization. The obtainedpowder had a melting point of 212° C. similar to that of polyamide 6, acrystallization temperature of 171° C., and a molecular weight of41,700. From scanning electron microscope observation, polyamide 6powder had a true spherical shape and a fine particle shape with asmooth surface, a number average particle size of 6.1 μm, a particlesize distribution index of 1.34, a sphericity of 93, and a linseed oilabsorption of 53 mL/100 g. Table 1 shows the properties of the obtainedpolyamide 6 fine particles.

Example 7

Polymerization was carried out in the same manner as in Example 1 exceptthat the polyethylene glycol was changed to a polyethylene glycol (WakoPure Chemical Industries, Ltd., first grade polypropylene glycol 2,000,molecular weight 3,600, SP value 18.7) to obtain 2.3 g of a powder. Thesolution was a homogeneous solution at the start of polymerization and asuspension after polymerization. The obtained powder had a melting pointof 216° C. similar to that of polyamide 6, a crystallization temperatureof 170° C., and a molecular weight of 38,000. From scanning electronmicroscope observation, polyamide 6 powder had a true spherical shapeand a fine particle shape with a smooth surface, a number averageparticle size of 21.5 μm, a particle size distribution index of 1.92, asphericity of 91, and a linseed oil absorption of 65 mL/100 g. Table 1shows the properties of the obtained polyamide 6 fine particles.

Example 8

Polymerization was carried out in the same manner as in Example 1 exceptthat the polytetramethylene glycol was changed to a polyethylene glycol(Wako Pure Chemical Industries, Ltd., first grade polytetramethyleneglycol 2,000, molecular weight 7,500, SP value 17.9) to obtain 2.3 g ofa powder. The solution was a homogeneous solution at the start ofpolymerization and a suspension after polymerization. The obtainedpowder had a melting point of 214° C. similar to that of polyamide 6, acrystallization temperature of 169° C., and a molecular weight of40,200. From scanning electron microscope observation, polyamide 6powder had a true spherical shape and a fine particle shape with asmooth surface, a number average particle size of 31.5 μm, a particlesize distribution index of 2.76, a sphericity of 90, and a linseed oilabsorption of 63 mL/100 g. Table 1 shows the properties of the obtainedpolyamide 6 fine particles.

Example 9

1.7 g of adipic acid (manufactured by Tokyo Chemical Industry Co., Ltd.,SP value 25.4), 2.2 g of a 50% aqueous solution of hexamethylenediamine(manufactured by Tokyo Chemical Industry Co., Ltd., SP value 19.2), 6 gof polyethylene glycol (first grade polyethylene glycol 20,000,molecular weight 18,600, manufactured by Wako Pure Chemical Industries,Ltd.), and 2.6 g water as a solvent were added to a 100 mL autoclave,and after sealing the autoclave, replacement with nitrogen was performedup to 10 kg/cm². The system pressure was adjusted to 0.1 kg/cm² whilereleasing nitrogen, and then the temperature was raised to 260° C. Atthis time, after the system pressure reached 17.5 kg/cm², the pressurewas controlled while slightly releasing the pressure to maintain 17.5kg/cm². After the temperature reached 260° C., polymerization wasstarted by releasing the pressure at a rate of 0.6 kg/cm² min. At thispoint, the inner solution was uniformly transparent. While raising thetemperature to 280° C., the pressure in the system was reduced to 0, andat the same time, heating was maintained while flowing nitrogen for 1hour to complete polymerization. After polymerization, the innersolution was suspended. The obtained slurry was filtered, and 40 g ofwater was added to the filtered product, followed by washing at 80° C. Aslurry liquid without an aggregate filtered through a 200 μm sieve wasthen filtered again and the filtered product isolated was dried at 80°C. for 12 hours to obtain 2.3 g of powder. There were no aggregatesgreater than 200 μm. The obtained powder had a melting point of 267° C.similar to that of polyamide 66, a crystallization temperature of 211°C., and a molecular weight of 73,600. From scanning electron microscopeobservation, polyamide 66 powder had a true spherical shape and a fineparticle shape with a smooth surface, a number average particle size of6.5 μm, a particle size distribution index of 1.60, a sphericity of 91,and a linseed oil absorption of 56 mL/100 g. FIG. 3 shows a scanningelectron micrograph (magnification×1,500) of the true sphericalpolyamide 66 fine particles. The SP value of polyamide 66 is 20.6. Table2 shows the properties of the obtained polyamide 66 fine particles.

TABLE 2 Compar- Compar- Compar- Compar- Compar- Exam- Exam- Exam- Exam-ative Ex- ative Ex- ative Ex- ative Ex- ative Ex- ple 9 ple 10 ple 11ple 12 ample 1 ample 2 ample 3 ample 4 ample 5 Polyamide constitutingpoly- poly- poly- poly- — — poly- — — polyamide fine particles amide 66amide 6 amide 12 amide 12 amide 6 Weight average molecular 73,600 21,000110,000 50,000 — — 34,400 — — weight of polyamide constituting polyamidefine particles Number average particle (μm) 6.5 13.1 6.6 6.0 — — 18.0 —— size of polyamide fine particles Sphericity of polyamide 91 92 94 96 —— 68 — — fine particles Particle size distribution 1.60 1.54 1.37 1.30 —— 1.30 — — index of polyamide fine particles Linseed oil adsorption(mL/100 56 60 54 58 — — — — — amount of polyamide g) fine particlesMelting point of polyamide (° C.) 267 216 173 175 — — 210 — — fineparticles Crystallization temperature (° C.) 211 170 139 136 — — 165 — —of polyamide fine particles

Example 10

4 g of aminohexanoic acid (manufactured by Wako Pure ChemicalIndustries, Ltd., SP value 17.5), 6 g of polyethylene glycol (firstgrade polyethylene glycol 6,000, manufactured by Wako Pure ChemicalIndustries, Ltd.), and 10 g of water as a solvent were added to a 100 mLautoclave, and after forming a homogeneous solution, the autoclave wassealed, and replacement with nitrogen was performed up to 10 kg/cm². Thesystem pressure was adjusted to 0.1 kg/cm² while releasing nitrogen, andthen the temperature was raised to 240° C. At this time, after thesystem pressure reached 10 kg/cm², water vapor was controlled to beslightly released so that the pressure was maintained at 10 kg/cm².After the temperature reached 240° C., polymerization was started byreleasing the pressure at a rate of 0.2 kg/cm² min. While raising thetemperature to 255° C., the pressure in the system was reduced to 0, andat the same time, heating was maintained while flowing nitrogen for 3hours to complete the polymerization. After polymerization, the innersolution was suspended. Nitrogen was again filled to 10 kg/cm² and thencooled to room temperature. Water was added to the obtained solid andheated to 80° C. to dissolve the dissolved matter. The obtained slurrywas filtered, and 40 g of water was added to the filtered product,followed by washing at 80° C. A slurry liquid without an aggregatefiltered through a 200 μm sieve was then filtered again and the filteredproduct isolated was dried at 80° C. for 12 hours to obtain 1.4 g ofpowder. There were no aggregates greater than 200 μm. The obtainedpowder had a melting point of 216° C. similar to that of polyamide 6, acrystallization temperature of 170° C., and a molecular weight of21,000. From scanning electron microscope observation, polyamide 6powder had a true spherical fine particle shape, a number averageparticle size of 13.1 μm, a particle size distribution index of 1.54, asphericity of 92, and a linseed oil absorption of 60 mL/100 g. Table 2shows the properties of the obtained polyamide 6 fine particles.

Example 11

Polymerization was carried out in the same manner as in Example 10except that aminohexanoic acid was changed to aminododecanoic acid(manufactured by Wako Pure Chemical Industries, Ltd., SP value 17.2) andthat a polyethylene glycol with a different molecular weight (firstgrade polyethylene glycol 20,000 manufactured by Wako Pure ChemicalIndustries, Ltd.) was used, to obtain 0.8 g of powder. A homogeneoussolution was formed from the time when the temperature was raised to100° C. or higher, and the solution was a suspension afterpolymerization. The obtained powder had a melting point of 173° C.similar to that of polyamide 12, a crystallization temperature of 139°C., and a molecular weight of 110,00. From scanning electron microscopeobservation, polyamide 12 powder had a true spherical shape and a fineparticle shape with a smooth surface, a number average particle size of6.6 μm, a particle size distribution index of 1.37, a sphericity of 94,and a linseed oil absorption of 54 mL/100 g. FIG. 4 shows a scanningelectron micrograph (magnification×1,000) of the true sphericalpolyamide 12 fine particles. Table 2 shows the properties of theobtained polyamide 12 fine particles.

Example 12

Polymerization was carried out in the same manner as in Example 11except that 2 g of the aminododecanoic acid and 8 g of the polyethyleneglycol were used, to obtain 1.2 g of powder. The obtained powder had amelting point of 175° C. similar to that of polyamide 12, acrystallization temperature of 136° C., and a molecular weight of50,000. From scanning electron microscope observation, polyamide 12powder had a true spherical shape and a fine particle shape with asmooth surface, a number average particle size of 6.0 μm, a particlesize distribution index of 1.30, a sphericity of 96, and a linseed oilabsorption of 58 mL/100 g. Table 2 shows the properties of the obtainedpolyamide 12 fine particles.

Comparative Example 1

Polymerization was carried out in the same manner as in Example 1 exceptthat the polyethylene glycol was changed to dimethyl silicone oil(manufactured by Shin-Etsu Chemical Co., Ltd. KF-96H, 10,000 cs,molecular weight 88,400, SP value 14.5) and the water used for washingwas changed to toluene. The liquid was separated into two phases at thestart of polymerization, and remained coarsely separated into two phasesof silicone and polyamide after polymerization. Washing was performedusing toluene, but 3.2 g of polyamide aggregates were recovered over 200μm, and no particles were obtained.

Comparative Example 2

Polymerization was carried out in the same manner as in Example 1 exceptthat the polyethylene glycol was changed to polystyrene (manufactured byAldrich Japan Inc., polystyrene Mw=280,000, molecular weight 278,400, SPvalue 16.6) and the water used for washing was changed to toluene. Theliquid was separated into two phases at the start of polymerization, andremained coarsely separated into two phases of polystyrene and polyamideafter polymerization. Washing was performed using toluene, but 3.3 g ofpolyamide aggregates were recovered over 200 μm, and no particles wereobtained.

Comparative Example 3

To a reaction vessel equipped with a stirrer, 355 mL of liquid paraffin,109 g of ε-caprolactam, 0.6 g of N,N′-ethylenebisadearaamide, and 0.5 gof fine silica were added and the mixture was stirred at 650 rpm. Avessel was heated to 100° C. and 31 mL of liquid paraffin was distilledoff under a vacuum of 200 torr to remove residual moisture. Afterreturning the system to atmospheric pressure, 0.5 g of sodium hydridewas added under nitrogen inflow and the vessel was sealed, followed bystirring for 60 minutes. After raising the temperature to 110° C., thetemperature was raised to 130° C. over 1 hour to start polymerization,and at the same time, 2.9 g of stearyl isocyanate was fed into thesystem through a pump at a rate of 0.02 g/min. The solution wassuspended at the start of polymerization. The polymerization wascontinued for 2 hours after raising the temperature to 130° C. tocomplete the polymerization. After cooling the temperature to roomtemperature and washing liquid paraffin with toluene, 85 g of powder wasobtained. The obtained powder had a melting point of 210° C. similar tothat of polyamide 6, a crystallization temperature of 165° C., and amolecular weight of 34,400. From scanning electron microscopeobservation, polyamide 6 powder had an irregular fine particle shape, anumber average particle size of 18.0 μm, a particle size distributionindex of 1.30, and a sphericity of 68. FIG. 5 shows a scanning electronmicrograph (magnification×1,000) of the irregular polyamide 6 fineparticles. Table 2 shows the properties of the obtained polyamide 6 fineparticles.

Comparative Example 4

Polymerization was carried out in the same manner as in Example 10except that water was not used. The liquid was separated into two phasesat the start of polymerization, and after the polymerization, the liquidwas roughly separated into two phases of polyamide 6 and polyethyleneglycol, and polyamide 6 particles were not obtained.

Comparative Example 5

Polymerization was carried out in the same manner as in Example 11except that water was not used. The liquid was separated into two phasesat the start of polymerization, and after the polymerization, the liquidwas roughly separated into two phases of polyamide 12 and polyethyleneglycol, and polyamide 12 particles were not obtained.

INDUSTRIAL APPLICABILITY

The polyamide fine particles having a spherical shape, a smooth surface,a narrow particle size distribution, and a high crystallizationtemperature have high heat resistance and chemical resistance inherentin polyamides with a high crystallization temperature, as well asslipperiness due to a spherical and smooth surface with a narrowparticle size distribution, and therefore can be suitably utilized forpaints, adhesives, inks, toner light diffusing agents, liquid crystalspacers, matting agents, additives for polymer alloy, carriers for avariety of catalysts, chromatographic carriers, automotive parts,aircraft parts, electronic parts, cosmetic additives, medical carriersand the like. The polyamide fine particles can be applied to ahigh-performance paint that can be used under harsh conditions underwhich a conventional paint is unusable or the like due to heatresistance derived from a high crystallization temperature, a truespherical and smooth surface form, and a uniform particle diameter.Furthermore, in cosmetic applications, the amide group concentration inpolyamide is increased so that the moisture retention is increased, andit is possible to achieve both a smooth and uniform feel and a moistfeeling due to the true spherical shape and uniform particle size.

What is claimed is:
 1. Polyamide fine particles having a number averageparticle size of 0.1 to 100 um, a sphericity of 90 or more, a particlesize distribution index of 3.0 or less, a linseed oil absorption of 100mL/100 g or less, and a crystallization temperature of 150° C. or more,wherein polyamide constituting the polyamide fine particles is any oneselected from polyamide 6, polyamide 66, and a copolymer thereof.
 2. Thepolyamide fine particles according to claim 1, wherein the weightaverage molecular weight of polyamide constituting the polyamide fineparticles is 8,000 or more.
 3. The polyamide fine particles according toclaim 1, wherein the linseed oil absorption is 90 mL/100 g or less.